The invention relates to a signal generator for synthesizing television test line signal variations having a relatively high frequency and being composed of individual portions.
Signals having a relatively high frequency, particularly television test line signals which are coupled to a reference signal having a low frequency have been generated so far by means of conventional analogue techniques. The difficulty encountered herewith, particularly for television test line signals, is that they are partly composed of a large number of different signal components (FIGS. 6a and 6b). Generating these test line signals by means of the analogue technique, primary signals having a defined rise time are, for example, generated first and brought by means of very expensive and complicated band limiting filters to the required definite variation (white pulse, 2T-pulse, 20T-LF-component). In addition, special analogue signal generators, such as staircase voltage generators are required. Finally, modulators and analogue adding circuits are required to generate the 20T-colour carrier component and to superimpose this component on the LF-component or to obtain a staircase signal having a carrier. Finally, all these signal components which are individually generated must be combined in a selection and combination circuit into the prescribed definite test line signal. In addition, it is required that each signal component generator out of a large plurality of signal component generators must be synchronized by a reference signal having a low frequency (in this case the television synchronizing signal) so that the relevant generator does not only have an extreme amplitude stability in spite of a phase which is, each time, different with respect to the reference signal, but also an excellent time stability, in order to perform its function as test line generator.
The type of signal generator described above and corresponding to the prior art is expensive and complicated, particularly owing to peripheral conditions which form an extra difficulty; besides that the equipment is rather bulky.